upgrade: rename `_copyrevlogs` to `_clonerevlogs`

The underlying revlog method is named `clone`, keeping the naming consistent
seems clearer. This is motivated to clarify the difference with an (upcoming)
function that simply copy revlog files as is.

mercurial/upgrade.py

@@ -533,7 +533,7 b' def _revlogfrompath(repo, path):'
         #reverse of "/".join(("data", path + ".i"))
         return filelog.filelog(repo.svfs, path[5:-2])
 
-def _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse, forcedeltabothparents):
+def _clonerevlogs(ui, srcrepo, dstrepo, tr, deltareuse, forcedeltabothparents):
     """Copy revlogs between 2 repos."""
     revcount = 0
     srcsize = 0
@@ -745,7 +745,7 b' def _upgraderepo(ui, srcrepo, dstrepo, r'
         deltareuse = revlog.revlog.DELTAREUSEALWAYS
 
     with dstrepo.transaction('upgrade') as tr:
-        _copyrevlogs(ui, srcrepo, dstrepo, tr, deltareuse,
+        _clonerevlogs(ui, srcrepo, dstrepo, tr, deltareuse,
                      're-delta-multibase' in actions)
 
     # Now copy other files in the store directory.